Project Summary Quantitation of viral load in peripheral blood is the primary means to detect impending Epstein-Barr virus (EBV)-associated disease. EBV is an important pathogen and results in considerable cost to the health care system. EBV is the causative agent of infectious mononucleosis as well as nasopharyngeal carcinoma, Burkitt?s lymphoma, and other B-cell lymphomas in immunosuppressed individuals. Although much has been learned about EBV from studies of in vitro transformed B-lymphoblastoid cell lines, critical gaps in knowledge regarding EBV pathogenesis in vivo remain to be answered, including how EBV persists in spite of the continuous immune surveillance. Current methods (i.e., quantitative PCR) to measure viral load suffer from a number of limitations that include: (1) being labor-intensive, (2) variability in pre-PCR steps (i.e., DNA extraction method used; use of whole blood, peripheral blood mononuclear cells, or enriched cell subpopulations), and (3) method of normalization (i.e, GAPDH, ?-globin, etc). The goal of this project is to develop a rapid method to detect EBV+ cells in peripheral blood at the single cell level using flow cytometry. This test will be rapid (<1 hr) and maintain cell morphology and phenotype. This test will be useful in research and clinical settings.